Method of and apparatus for recording and reproducing electrical impulses



Dec. 20, 1932.

R. E. RUTHERFORD METHOD. OF AND APPARATUS FOR RECORDING AND REPRODUCINGELECTRICAL IMPULSES Original Filed Dec. 20, 1928 Patented Dec. 20, 1932UNITED STATES,

PATENT OFFICE ROBERT E. RUTHERFORD, OF IPHILADIEH'JPHIA, PENNS Y LVANIAMETHOD OF AND APPARATUS FOR RECORDING AND REPRODUCING ELECTRICALIMPULSES Application filed December 20, 1928, Serial No. 327,333.Renewed July 29, 1932.

My invention relates to the recording of electrical impulses, andparticularly to the electrical recording of sound.

An objectof my invention is to provide a new and simple method of soundrecordation.

Another object of my invention is to provide a means of recording anysuccession of electrical impulses, as for example telegraph ortelevision signals.

Still another object of my invention is to provide a method of recordinsounds, which is substantially free from e ects producing subsidiary orinterferent noises.

A further object of my invention is to provide an inexpensive andpractically permanent sound record.

My invention possesses other objects and valuable features, some ofwhich will be set forth in the following description of my inventionwhich is illustrated in the drawing forming part of the specification.It is to be understood that I do not limit myself to the showing made bythe said description and drawing, as I may adopt varying forms of myinvention within the scope of the claims.

Referring to the drawing:

Figure 1 is a plan View of an electrical recorder and reproducerembodying my invention.

Figure 2 is a longitudinal sectional View of the apparatus shown inFigure 1, the

- plane of section being on the line 2-2 of Fig. 1. The electricalcircuits used in recording and reproducing sound are diagrammaticallyshown in this figure.

Considered broadly, my invention comprises the recording of electricalimpulses by electrizing a dielectric,and their reproduction byafl'ecting an electrostatically sensitive relay by the electrizeddielectric.

Electrostatic charges are usually of a temporary character and dissipatethemselves or are discharged within a short time. It has been known forsome years, however, that it is. possible to produce permanentelectrical charges upon certain dielectrics, and for this processtheterm electrization has been proposed and has come to be generallyaccepted as meaning a permanent electrification.

While electrization of some dielectrics may be produced by bombardmentwith cathode rays, the more convenient method is to allow a liquid ormolten dielectric. to solidify'in an electrostatic field. Mostdielectrics are better conductors in a liquid than in a solid state, andit appears probable that ions are formed in the liquid dielectric whichcannot recombine and neutralize their charges when the materialsolidifies. This phenomenon has been observed in such dielectrics asbeeswax, resins, carnauba wax, shellac, parafiin, and various mixtures6of these and other ingredients. Whatever the mechanics of the effect-maybe, it is known that the electrization remains sensibly constant forperiods of several years, or as long as the effects have been underobservation. These elfects are utilized in my method of electricalrecording.

In the form of my invention which I have chosen for detaileddescription, the impulses to be recorded are sound waves translated intoelectrical impulses by the microphone 1 which'feeds into a speechamplifier 2. The entire recording apparatus is mountedon a groundedmetal base 6. The record is formed on a paper strip or tape 7, which isimpreg nated with a dielectric such as parafiin having a suitablemelting point, i. e., one higher than the ambient temperatures to whichit may be subjected but not so high as to injure the paper. In makingthe record the tape is transferred from a feed reel 8 to a receivingreel 9, the reels being journaled respectively on the standards 11 and12 mounted on opp0 site ends of the base 6.

The tape is drawn thru the apparatus by a pair of rubber covered rollers13 and 14, which are fixed to the shafts 16 and 17, journaled in thebracket 18. A pulley 19 on the shaft 16 is geared to the motor 21 by thebelt 22 and drive pulley 23. A smaller pulley 24, fixed to the shaft 17,drives-the recelving reel 9 by means of the slip-belt 26 and pulley 27on the reel shaft 28. The speed of the tape is thus determined by theroller 14, but the tape is constantly kept taut by the reel9, whosetendency to over-run is compensated for by the slipping of the belt 26.

Adjacent the feed reel 8 the tape runs under a guide wheel 31 and thenceover an electrical heating element 32 mounted on a bracket 33 secured tothe base. Closely adjacent the heating element is a hollow platen 34supplied with inlet and outlet pipes 36 and 37 thru which water or coldbrine may be circulated. It will thus be seen that as the tape is runthru the machine, the dielectric is melted by the heater and thenquickly chilled by the cooling platen.

Mounted above the platen on the insulating pillars 38 is a conductingplate 39, spaced above the platen just sufiiciently to allow the easypassage of the tape therebetween. This plate is connected to the platecircuit of the output tube of the speech amplifier 2, which is actuatedby the electrical impulses to be recorded. A strong variableelectrostatic field is therefore established between the plate and theplaten, which is grounded to the base and hence connected to thegrounded side of the amplifier output circuit.

It will be seen that as the tape is rapidly and uniformly drawn thru theapparatus, there is a fixed position or narrow line determined by thecritical temperature of the dielectric within the field at whichsolidification and electrization of the dielectric occurs. The fieldatthis position changes with the incoming electrical impulses, and thesuccessive elementary areas of the dielectric are differentiallyelectrized in correspondence with the successive impulses. The use of afairly wide conductor plate and platen maintains the, line ofsolidification in the electrostatic field during minor temperaturevariations.

The fixed charges due to the electrization have a maximum value of thesame order of magnitude as the maximum temporary charges which can beproduced by friction. P

The formation of such temporary charges can be largely suppressed andanomalous results prevented by metallizing the grounded surface 41 ofthe paper strip or otherwise rendering it conducting. This appears tohave an additional advantage in rendering the electrization morepermanent, but altho it is a desirable expedient, it is not an essentialone.

The reproducing e uipment is shown as mounted on the same ase 6 as therecorder. This comprises a pair of insulating brackets 46 which carry apair of conductors 47 and 48, connected to the filament 49 and grid 51,respectively, of anamplifier 52 which feeds a loudspeaker 53. The formof the conductors is not important as long as their opposed area issmall, so that they form a ca acity presenting a substantially line surace to the record tape. They may be merely a pair of parallel wiresbetween which the tape is drawn, but I prefer to use rollers of smalldiameter as shown, with the upper or grid roller 48 pressed downwardagainst the tape by springs 54.

It is not contemplated'that the recordin and reproducing systems willusually be use simultaneously, altho this is sometimes done for thepurpose of monitoring the record. It is of course apparent that recorderand reproducer can be mounted entir ly separately, if desired.

In reproduction the electrized dielectric is drawn between thereproducing electrodes at substantially the same speed as for recording.The electrostatically sensitive vacuum tube relay is affected by thedifferentially electrized tape within the field of the conductors, andthe original impulses are reproduced in its output circuit, to betranslated into sound by the loudspeaker.

Practically all incidental orinterferent noise can be eliminated in thisdevice. By making the only parts which touch the record before it passesthru the reproducing capacitor of metal, substantially all tem oraryelectrical charges are removed, and t ese are the chief possible sourceof interference. When the tape is reeled up, such temporary charges asmay have been accumulated are dissipated by the conducting surface ofthe dielectric.

I claim:

L-The step in the method of recording sound impulses which compriseselectrizing a dielectric.

2. The method of recording sound which comprises the translation of thesound into electrical impulses, and electrizing a dielectric therewith.

3. The method of recording sound impulses which comprises electrizingelementary areas of a dielectric in correspondence with the potentialsto be recorded.

4. The method of recording sound imulses which comprises establishing anelectrostatic field correspondin to said impulses. and causing a moltendiefectric to solidify within said field.

5. The method of recording electrical impulses which comprisesestablishing an electrostatic field corresponding to'said impulsesbringing a molten dielectric within said field by a relative motiontherebetween, and cansing the dielectric to solidify within said field.

6. The method of recording sound impulses which comprises electrizingsuccessive elementary areas of a dielectric in correspondence with thesuccessive impulses to be recorded.

7. A'recorder for electrical impulses comprising means for establishingan electrostatic field corresponding to said impulses, means for causinga relative movement between said field and a dielectric, means formelting a portion of the dielectric, and means for causing thesolidification of the melted dielectric within the field.

8. A recorder for electrical impulses com-- prising means forestablishing an electrostatic field corresponding to said impulses,means for moving a dielectric-thru said field,

means for melting a rtion ofthe dielectric,

and means for causing the solidification of the melted dielectric withinthe field.

9. A recorder for electrical impulses comprising'a heater, a cooleradjacent thereto,

means for moving a dielectric past said heaterand cooler, and means forestablishing an electrostatic field thru the dielectric within the fieldof action of the cooler.

10. A record of sound impulses comprising an electrized dielectric.

11. A record of sound impulses comprising a differentially electrizeddielectric.

12. A record of sound impulses comprising a paper impregnated with anelectrized dielectric.

13. A record of sound impulses comprising a paper having a conductingsurface and impregnated with an electrized dielectric.

14. The method of reproducing electrical impulses which comprisescausing electrized areas of a dielectric successively to actuate anelectrically sensitive detector.

15. The method of reproducing sound which comprises causing successiveelementary electrized areas of a dielectric, to actuate an electricallysensitive detector to produce electrical impulses, and translating saidimpulses into sound.'-

and means for util ,a dielectric in intensities 16. A phonographicmethod comprising means for translating the sound into electricalimpulses, means for successively electrizing elementary areas of adielectric with said impulses, and means for reproducing the sound fromthe record thus formed. i 17. A sound reproducing system comprising anelectrized dielectric, a pair'of opposed conductors bringing successiveelementary areas of the dielectric Within the field of the condenser, anelectrostatically sensitive detector havingan actuatingcircuit connectedto said condenser,

said heating means for cooling said strip, and a plate Insulated fromsaid heating and cool- 111g means positioned to establish anelectrotion.

19. The method of recording sound which comprises electrizingdistributed areas along proportional to the sound impulses.

. In testimony whereof, I have hereunto set my hand. ROBERT E.RUTHERFORD.

forming a condenser, means for p ing the output of said detector toproduce sound. 18. A recorder for'electrical impulses comprising meansfor moving a dielectric strip, means for heating said strip, meansadjacent static field thru said strip in the cooling por- Y

